Method of manufacturing hard metal alloys



Patented on 25, 1938 UNITED STATES PATENT OFFICE METHOD OF MANUFACTURING.HARD

DIETAL ALLOYS Richard Kiefier, Reutte, Austria, assignor to The AmericanCutting Alloys, Inc., New York, N. Y., a corporation of Delaware I NoDrawing.

Application March 27, 1936,

Serial No. 71,183

4 Claims. (Cl. 75-137) This invention relates to a method ofmanufacturing hard metal alloys consisting of one or more carbides whichform the major portion of the alloyand are cemented by auxiliary metal"which are subjected in operation to mechanical wear.

The carbides involved are preferably those of tungsten, tantalum,columbium, zirconium,

boron, silicon, molybdenum, vanadium; chromium which are known as hardand wear resistant while the auxiliary metal substantially taken fromthe iron group may be supplemented bysome chromium.

It is one object of the invention-to simplify .this manufacture.

. It is another object of this invention to render the manufacturecheaper and more efiicient.

Up to date the carbides to be used for the hard alloy have been obtainedby combining the proper amount of carbon with the desired element.

For this purpose, the element had to be separated the manufacture of thehard alloys diillcult and expensive.

According to this invention, at least the carbides to be used in thehard alloy are obtained immediately by proper treatment of the ores inwhichthe elements are contained which are to be carburized. To thiseffect, the ores are mixed with carbon, or carbon containing substances,in such an amount as to suffice at least for transforming the element ifpresent in the form of a compound in the ores, into its metallic stateand immediately afterwards, and in the same operation, into the desiredcarbide. Consequently,

element to be carburized is present in the ores. The amount of carbonnecessary for reducing the element if present in an oxygen-combinationis to be ascertained, and then the further first the state is to beascertained in which the.

thus reduced element. This total amount of carbon, advantageously withsome excess, is then admixed to the ores which are heated so as toseparate the elements, or their compounds, from the ores and to reducethem, if they are presentin an oxidized state, and furthermore tocarburize them. It is done, according to this invention, in a singlestep, whereupon the carbide so obtained is separated from the remaindersof the ores.

One may proceed also in such a way that both the necessary carbonamount, or a slight excess,

and the auxiliary metal are admixed to the ores containing the elementsto be carburized, and the mixture is then heated to' form carbide mixedwith auxiliary metal, which is then separated from the remainders of theores and permitted to solidify.

One may also proceed in such a way that the ores containing the desiredelement, or elements, to be carburized and ores containing some or allauxiliary metal are mixed, thereupon heated, so that a melt is obtainedcontaining the auxiliary metal and the elements to be carburized,whereby carburization of these elements is done by means of the carbonadmixed, whereupon the mixture is separated from the remainders of theores and permitted to solidify. In case the auxiliary metal is presentin its ores also in an oxidized state, additional carbon is to beadmixed to the ores suiiicient to reduce also the oxides of theauxiliary metal when separating from the ores.

The alloy so obtained is regularly a cast one. It is sometimes advisableto increase its density and toughness thereby that one comminutes thealloy thus obtained to a desired fineness, presses the mixture into adesired shape, and solidifies it again by heat treatment advantageouslybelow melting temperature, i. e., regularly high sinternan.

The separation of the oxides contained in the ores may be done attemperatures equivalent to melting temperature or only to a temperatureat which these compounds become plastic but ready to combine with thecarbon present.

If it is intended to manufacture a hard metal alloy consisting of amajor portion of tungsten carbide (WC or W2C) and iron, one may startfrom the ore Ferberite' containing approximately to tungsten trioxideand 20 to 25% iron.

-If the ores contain sulphur, or other impurities,

they are advantageously heated up to about 500 C. whereby the sulphurand other impurities evaporating at, or below, this temperature aredriven off. It is furthermore advisable to comminute or to pulverize theores although it is not necessary as a rule. To these ores carbon isadmixed in sufficient amount to reduce the tung- 5 sten trioxide intometallic tungsten and to carburize immediately the metallic tungstenthus obtained. Although it is not correct in the extreme scientificsense one may say that according to this invention the compounds of thel e1ements to be carburized are separatedv from the ores, reduced andcarburized in situ. The great advantage of the invention over all theprocesses previously used appears therefrom.

It is not only economic but also extremely ef-.

l ficient. In such a way, both WC and W2C may be formed. In the firstcase, care has to be taken that the temperature is not elevated so highthat the WC decomposes again. It is well known to the art that WC whenmelted decomposes and 30 therefore temperatures corresponding only to aplastic state of the WC are to be applied. Preferably, temperatures nearto about 2000 C. are to be applied. Regularly, the ferberite is meltedat such tem- 5 peratures, including the iron contained therein. Thedross formed is lighter than the metals, or their compounds obtained andswims upon them. Therefore, this dross can easily be removed. One maypermit, however, the entire material in- ;0 cluding the dross also tocool down and tosolidifyvated pressure. In such case, the tungsten maybe carburized already at. temperatures between about 1000 and 1200 C.,while still in a solid state, and if performing such treatment longenough, through several hours, if need be, then the transformation ofthe tungsten in a still solid state into the tungsten monocarbide can beperformed. At slightly elevated temperature 0 up to about 1400 to 15000., also the iron will be melted, so that a desirable alloy containingapproximately 74% to 80% tungsten monocarbide and 25% to iron can beobtained. By addition of iron the amount of thisauxiliary metal in thealloy can be increased. By addition of another ore containing tungstenbut not iron, or iron in a lower proportion, the amount of tungstencarbide in the final alloy can be increased and that of the irondecreased. Due to the pres- D ence of the iron in a molten state themelting temperature of tungsten monocarbide formed is materiallyreduced, from about 2800 C. close to about 2000 C. Consequently, it isadvisable not to exceed substantially the temperatures at which 5 thiscarbide is formed and which lie, in general, above about 1000 C. up toabout 2000 C. It is to be understood that the carburization of thetungsten within this temperature range is performed while this tungstenis still in a solid state,

) and that the carbide formed is also in a solid' state in spite of themelted iron present. If raising, however, the temperature substantiallyabove 2000 C., then the tungsten carbide would melt in the presence ofthe molten iron, and decompose into tungsten dicarbide and free carbon.

Instead of treating the ores in the presence of carbon in a gaseousstate, solid carbon such as lamp black may be admixed, or both solid andgaseous carbon may be used.

Hard alloys thus obtained are of a high but not the same purity thanother known hard alloys manufactured by cautiously carburizing puremetallic tungsten, mixing it with a pure auxiliary metal and sinteringthe mixture in a hydrogen atmosphere. However, the hard alloy obtainedaccording to the invention is of suflicient hardness and toughness foruse in drills and tool elements for squaring, as stone auger and in allor while in its ores, if desired. The amount of chromium may be betweenabout 1 to 2%, or

more.

One may also start from wolframite containing about 75% W0: and iron. Itis to be treated in the same way as described above, rendering a hardalloy, containing between about 70% to 75% W2C (or WC), balance iron andmanganese.

Starting from the ore hybnerite, containing approximately 75% to 77% W03and 23% to 25% manganese, one obtains in the way described above fromferberite an alloy consisting of about 75% to 83% W20, or WC, balancemanganese.

Due to the fact that tungsten. possesses the greater affinity to carbon.than iron, or manganese, during the heat treatment tungsten carbide isformed while iron, or manganese, remains uncombined, provided that theamount of carbon admixed, or permitted to pass in gaseous form into thefurnace, is properly measured. It add-- ing carbon in such an excessthat also the auxiliary metal can be carburized, then an extremely hardbut also tough alloy can be obtained.

By the addition of chromium, the hardness of the auxiliary metalcementing the carbides will be increased.

By using nickel, the hardness of the alloy is somewhat decreased but itsstrength and toughness increased.

Ina similar way, other hard alloys may be manufactured. Thus, molybdenumcarbide may be obtained out of molybdenum glance. This ore may first beliberated of its sulphur and other impurities by heat treatment at about500 C. Thereupon carbon is admixed, in an amount sufiicient to reducethe molybdenum acid (M002) when separating from the ores and tocarburize it immediately afterwards (quasi in situ). Iron or cobalt, ornickel, containing ores are to be admixed to the molybdenum glance, ifan alloy is to be obtained containing one, or more, of these auxiliaryelements. All the ores, after being liberated from impurities by heattreatment up to 500 C. are mixed in. such a proportion that themolybdenum carbide and auxiliary metal are present in the desiredproportion in the final alloy.

Although the correct amount of carbon can be :alculated, it is better ineach of the cases reerred to above to establish the proper amounts )fcarbon by experiment. The contents of the iesired'element in the oresmay differ, so that he experimental way is to be preferred.

One proceeds in a similar way when a hard alloy is to be obtainedcontaining two or more :arbides and auxiliary metal. Thereby mixedcrystals of the carbide may be obtained. Then, however, the temperaturesare to be kept very near to melting temperature, and the treatment to becontinued for a suiilcient time. The treatment may be shorter if meltingof the carbides is permissible. I

If starting from ores which contain only the elements, or compoundsthereof, to be carburized but no auxiliary metal, then one may obtainalso hard bodies consisting only of carbide. They are, as it iswell-known to the art, relatively brittle.

It is preferable, therefore, to comminute such bodies, and to admixauxiliary metal, and to solidify the mixture in well-known manners.

As outlined above, it is not necessary that all the carbide is obtainedimmediately out of the ores. It satisfies the invention it only asubstantial part of such carbide is obtained in such a way. Furthermore,the auxiliary metal if used, may be either added in a metallic state, orin the form of a compound, or still in its ores.

Furthermore, if more than one carbide is to be included in the alloy,they may be obtained separately, or one carbide together with theauxiliary metal, and then the carbide may be mixed together in thedesired proportion and cemented with auxiliary metal.

If a hard alloy is desired consisting, or containing, titanium carbide,one may start, or add, from the ore rutile, or brookite, or anatase,containing approidmately 97% to 98% titanium oxide. The amount of carbonnecessary for reduction of this oxide and carburlzing of the reducedtitanium being calculated, or ascertained by experiment, one proceeds ina similar way as outlined above, including the addition of other carbideand auxiliary metal, as the case may be.

If a silicon carbide is to be obtained, or to be added, one starts froma silicate.

' If tantalum carbide is desired, one starts from tantalite.

o If boron carbide is desired, one starts from borax.

If vanadium carbideis desired, one starts from 1 petronite.

If columbium carbide is desired, one starts preferably from colombiteThe invention is not limited to any of the ex-' amples given herein.

It may be added that the carbon content may also be chosen so that onlypart of the reduced metal obtained out of the ores is carburized whilethe balance remains in a metallic state. One may obtain hereby forinstance an alloy containing tungsten carbide, molybdenum carbide,molybdenum in a metallic state, and an auxiliary metal. Similar resultsmaybe obtained from other ores and other carbides. Thus, for instance, ahard alloy may be made consisting of a major portion of tungsten carbidewhile the balance consists in: metallic m tungsten alone.

when hereinbefore a major portion of car bide, comprising one or morecarbides, is referred to, it amounts to over 50% by weight of the finalalloy, preferably about 60% to over 75%, up to 95% carbide, while thebalance conores containing oxides of said elements selected in desiredratio, in presence of carbon in an amount sufiicient to-reduce theoxides of said; hard carbide forming elements present in said ores andto convert the reduced elements-into.

' carbide, said heating performed to such an extent and temperature asto melt said ores and auxiliary metal and thereby to separate saidoxides from said ores, to reduce said oxides and to convert the elementsso obtained into carbide, thereupon separating the carbide thus obtainedfrom the remains of said ores, and comminuting and sintering saidcarbide in desired shape.

2. A method of producing a hard body containing auxiliary metal andcarbide of one to four elements capable offorming hard carbides, saidelements being tungsten, molybdenum, tantalum, titanium, silicon, boron,zirconium, columbium, so chromium, comprising the steps of heating amixture of auxiliary metal and one to four ores containing oxides ofsaid elements and selected in desired ratio, in presence of carbon in anamount sufliclent to reduce the oxides of said hard carbide formingelements present in said ores .and to convert the reduced elements intocarbide, said heating performed above about 1000 C. and at least atmelting temperature of said ores and auxiliary metal but below themelting temperao ture of carbide to be formed and to such an extent asto separate saidoxides from said ores, to reduce said oxides and toconvert the elements so obtained into carbide, to melt said auxiliarymetal and to alloy it with said carbide, and thereupon separating thealloy thus obtained from the remains of said ores, comminuting saidalloy and sintering it into desired shape.

3. A method of producing a hard body containing a. major portion ofcarbide of one to four elev ments capable of forming hard carbides, saidelements being tungsten, molybdenum, tantalum, titanium, silicon, boron,zirconium, columbium, chromium, and about 5% to 30% binding metalselected from a group consisting of iron, nickel, 5g.

cobalt, chromium, comprising the steps of heating said binding metal andone to fourores selected in desired ratio, in presence of carbon in anamount suflicient to reduce the oxides of said hard carbide formingelements present in said 00 ores and to convert the reduced elementsinto carbide, said heating performed above about1000 C. and at least atmelting temperature of said ores and binding 'metal but below themelting temperature of carbide to beformed and to such 5 an extent as toseparate said oxides from said ores, to reduce said oxides and toconvert the elements so obtained into carbide, and to. melt said bindingmetal, thereupon separating and solidifying the mixture of moltenbinding metal and carbide thus obtained from the remains of said ores,then comminuting and sintering said mixture in desired shape.

4. A method of producing a hard metal alloy consisting of about 70% to77% of tungsten car- ,z

1 0 and iron contained therein and simultaneously separating said oxidesfrom said ores, reducing said oxides and converting the tungsten soobtained into carbide, thereupon separating the mass substantiallyconsisting of tungsten carbide and iron thus obtained from the balanceof said ore, then allowing said mass to cool and thereupon comminutingand sintering said mass into desired shape.

RICHARD KIEFFER

